Backup power supplies are often used to supply power when a utility power grid is disabled. Internal combustion engine driven generators are often deployed as backup power supplies. These generators, however, are relatively large and noisy, and output toxic emissions.
Fuel cells are known to generate electrical power through chemical processes having relatively minimal emissions with little environmental impact. Accordingly, fuel cells have been explored as an attractive alternative to conventional backup generators. Unlike generators, however, fuel cells typically cannot be activated within a short period of time. Accordingly, in backup power applications, fuel cells often output electrical power continuously, regardless of whether the power grid is operational. In the event power is cut off, the fuel cell supplies backup power which can be distributed by the grid to critical components, or selected areas of the grid.
U.S. Pat. No. 6,700,804 describes a backup fuel cell coupled to a utility grid. The fuel cell supplies a DC voltage to an inverter, which, in turn, supplies an AC signal to a utility distribution system. However, the AC signal output from the inverter should be synchronized to the AC signal generated by the utility in order to assure compatibility with components connected to the distribution system. Moreover, the root mean square (rms) and phase of the AC inverter output relative to the utility AC signal should be controllable in order to maintain efficient power transmission, even when variations occur in the utility AC signal. Thus, a synchronizable and adjustable DC to AC conversion circuit is required to improve transmission characteristics.
The present disclosure is directed to overcome one or more of the shortcomings in the prior art.